An extensive search of Rootes factory literature (manuals, handbooks, advertising) has shown that Rootes NEVER called any of their cars "Phase" (even though the motoring press did). The only terms used were Mark and Series. The first iteration of a model (like the Hillman Minx) was the Mark 1, and facelifts were mark 2 etc. A major redesign became the Series 1 with subsequent facelifts being called Series 2,3 etc.

Hence, this should be called a Mark 1 Hillman Husky. Interestingly, there was never a Mark 2. The Husky was based on the Minx, and in 1956 Rootes released the Audax Minx, a major facelift the first iteration of which was the Series 1. So the next Husky was also a Series 1.

I don't have a strong opinion either way for Mark vs Phase. My fairly small selection of sources refer to Mark with no mention of Phase, so supporting lemansvk's argument. Just to be clear, our use of Series is correct from all the sources I have, so this is not part of the discussion.